/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.compression;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;

import java.util.List;
import java.util.zip.CRC32;
import java.util.zip.DataFormatException;
import java.util.zip.Deflater;
import java.util.zip.Inflater;

/**
 * Decompress a {@link ByteBuf} using the inflate algorithm.
 */
public class JdkZlibDecoder extends ZlibDecoder
{
    private static final int FHCRC = 0x02;

    private static final int FEXTRA = 0x04;

    private static final int FNAME = 0x08;

    private static final int FCOMMENT = 0x10;

    private static final int FRESERVED = 0xE0;

    private Inflater inflater;

    private final byte[] dictionary;

    // GZIP related
    private final ByteBufChecksum crc;

    private enum GzipState {
        HEADER_START, HEADER_END, FLG_READ, XLEN_READ, SKIP_FNAME, SKIP_COMMENT, PROCESS_FHCRC, FOOTER_START,
    }

    private GzipState gzipState = GzipState.HEADER_START;

    private int flags = -1;

    private int xlen = -1;

    private volatile boolean finished;

    private boolean decideZlibOrNone;

    /**
     * Creates a new instance with the default wrapper
     * ({@link ZlibWrapper#ZLIB}).
     */
    public JdkZlibDecoder()
    {
        this(ZlibWrapper.ZLIB, null);
    }

    /**
     * Creates a new instance with the specified preset dictionary. The wrapper
     * is always {@link ZlibWrapper#ZLIB} because it is the only format that
     * supports the preset dictionary.
     */
    public JdkZlibDecoder(byte[] dictionary)
    {
        this(ZlibWrapper.ZLIB, dictionary);
    }

    /**
     * Creates a new instance with the specified wrapper. Be aware that only
     * {@link ZlibWrapper#GZIP}, {@link ZlibWrapper#ZLIB} and
     * {@link ZlibWrapper#NONE} are supported atm.
     */
    public JdkZlibDecoder(ZlibWrapper wrapper)
    {
        this(wrapper, null);
    }

    private JdkZlibDecoder(ZlibWrapper wrapper, byte[] dictionary)
    {
        if (wrapper == null)
        {
            throw new NullPointerException("wrapper");
        }
        switch (wrapper)
        {
            case GZIP:
                inflater = new Inflater(true);
                crc = ByteBufChecksum.wrapChecksum(new CRC32());
                break;
            case NONE:
                inflater = new Inflater(true);
                crc = null;
                break;
            case ZLIB:
                inflater = new Inflater();
                crc = null;
                break;
            case ZLIB_OR_NONE:
                // Postpone the decision until decode(...) is called.
                decideZlibOrNone = true;
                crc = null;
                break;
            default:
                throw new IllegalArgumentException(
                        "Only GZIP or ZLIB is supported, but you used "
                                + wrapper);
        }
        this.dictionary = dictionary;
    }

    @Override
    public boolean isClosed()
    {
        return finished;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in,
            List<Object> out) throws Exception
    {
        if (finished)
        {
            // Skip data received after finished.
            in.skipBytes(in.readableBytes());
            return;
        }

        int readableBytes = in.readableBytes();
        if (readableBytes == 0)
        {
            return;
        }

        if (decideZlibOrNone)
        {
            // First two bytes are needed to decide if it's a ZLIB stream.
            if (readableBytes < 2)
            {
                return;
            }

            boolean nowrap = !looksLikeZlib(in.getShort(in.readerIndex()));
            inflater = new Inflater(nowrap);
            decideZlibOrNone = false;
        }

        if (crc != null)
        {
            switch (gzipState)
            {
                case FOOTER_START:
                    if (readGZIPFooter(in))
                    {
                        finished = true;
                    }
                    return;
                default:
                    if (gzipState != GzipState.HEADER_END)
                    {
                        if (!readGZIPHeader(in))
                        {
                            return;
                        }
                    }
            }
            // Some bytes may have been consumed, and so we must re-set the
            // number of readable bytes.
            readableBytes = in.readableBytes();
        }

        if (in.hasArray())
        {
            inflater.setInput(in.array(), in.arrayOffset() + in.readerIndex(),
                    readableBytes);
        }
        else
        {
            byte[] array = new byte[readableBytes];
            in.getBytes(in.readerIndex(), array);
            inflater.setInput(array);
        }

        int maxOutputLength = inflater.getRemaining() << 1;
        ByteBuf decompressed = ctx.alloc().heapBuffer(maxOutputLength);
        try
        {
            boolean readFooter = false;
            byte[] outArray = decompressed.array();
            while (!inflater.needsInput())
            {
                int writerIndex = decompressed.writerIndex();
                int outIndex = decompressed.arrayOffset() + writerIndex;
                int length = decompressed.writableBytes();

                if (length == 0)
                {
                    // completely filled the buffer allocate a new one and start
                    // to fill it
                    out.add(decompressed);
                    decompressed = ctx.alloc().heapBuffer(maxOutputLength);
                    outArray = decompressed.array();
                    continue;
                }

                int outputLength = inflater.inflate(outArray, outIndex, length);
                if (outputLength > 0)
                {
                    decompressed.writerIndex(writerIndex + outputLength);
                    if (crc != null)
                    {
                        crc.update(outArray, outIndex, outputLength);
                    }
                }
                else
                {
                    if (inflater.needsDictionary())
                    {
                        if (dictionary == null)
                        {
                            throw new DecompressionException(
                                    "decompression failure, unable to set dictionary as non was specified");
                        }
                        inflater.setDictionary(dictionary);
                    }
                }

                if (inflater.finished())
                {
                    if (crc == null)
                    {
                        finished = true; // Do not decode anymore.
                    }
                    else
                    {
                        readFooter = true;
                    }
                    break;
                }
            }

            in.skipBytes(readableBytes - inflater.getRemaining());

            if (readFooter)
            {
                gzipState = GzipState.FOOTER_START;
                if (readGZIPFooter(in))
                {
                    finished = true;
                }
            }
        }
        catch (DataFormatException e)
        {
            throw new DecompressionException("decompression failure", e);
        }
        finally
        {

            if (decompressed.isReadable())
            {
                out.add(decompressed);
            }
            else
            {
                decompressed.release();
            }
        }
    }

    @Override
    protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception
    {
        super.handlerRemoved0(ctx);
        if (inflater != null)
        {
            inflater.end();
        }
    }

    private boolean readGZIPHeader(ByteBuf in)
    {
        switch (gzipState)
        {
            case HEADER_START:
                if (in.readableBytes() < 10)
                {
                    return false;
                }
                // read magic numbers
                int magic0 = in.readByte();
                int magic1 = in.readByte();

                if (magic0 != 31)
                {
                    throw new DecompressionException(
                            "Input is not in the GZIP format");
                }
                crc.update(magic0);
                crc.update(magic1);

                int method = in.readUnsignedByte();
                if (method != Deflater.DEFLATED)
                {
                    throw new DecompressionException(
                            "Unsupported compression method " + method
                                    + " in the GZIP header");
                }
                crc.update(method);

                flags = in.readUnsignedByte();
                crc.update(flags);

                if ((flags & FRESERVED) != 0)
                {
                    throw new DecompressionException(
                            "Reserved flags are set in the GZIP header");
                }

                // mtime (int)
                crc.update(in, in.readerIndex(), 4);
                in.skipBytes(4);

                crc.update(in.readUnsignedByte()); // extra flags
                crc.update(in.readUnsignedByte()); // operating system

                gzipState = GzipState.FLG_READ;
            case FLG_READ:
                if ((flags & FEXTRA) != 0)
                {
                    if (in.readableBytes() < 2)
                    {
                        return false;
                    }
                    int xlen1 = in.readUnsignedByte();
                    int xlen2 = in.readUnsignedByte();
                    crc.update(xlen1);
                    crc.update(xlen2);

                    xlen |= xlen1 << 8 | xlen2;
                }
                gzipState = GzipState.XLEN_READ;
            case XLEN_READ:
                if (xlen != -1)
                {
                    if (in.readableBytes() < xlen)
                    {
                        return false;
                    }
                    crc.update(in, in.readerIndex(), xlen);
                    in.skipBytes(xlen);
                }
                gzipState = GzipState.SKIP_FNAME;
            case SKIP_FNAME:
                if ((flags & FNAME) != 0)
                {
                    if (!in.isReadable())
                    {
                        return false;
                    }
                    do
                    {
                        int b = in.readUnsignedByte();
                        crc.update(b);
                        if (b == 0x00)
                        {
                            break;
                        }
                    }
                    while (in.isReadable());
                }
                gzipState = GzipState.SKIP_COMMENT;
            case SKIP_COMMENT:
                if ((flags & FCOMMENT) != 0)
                {
                    if (!in.isReadable())
                    {
                        return false;
                    }
                    do
                    {
                        int b = in.readUnsignedByte();
                        crc.update(b);
                        if (b == 0x00)
                        {
                            break;
                        }
                    }
                    while (in.isReadable());
                }
                gzipState = GzipState.PROCESS_FHCRC;
            case PROCESS_FHCRC:
                if ((flags & FHCRC) != 0)
                {
                    if (in.readableBytes() < 4)
                    {
                        return false;
                    }
                    verifyCrc(in);
                }
                crc.reset();
                gzipState = GzipState.HEADER_END;
            case HEADER_END:
                return true;
            default:
                throw new IllegalStateException();
        }
    }

    private boolean readGZIPFooter(ByteBuf buf)
    {
        if (buf.readableBytes() < 8)
        {
            return false;
        }

        verifyCrc(buf);

        // read ISIZE and verify
        int dataLength = 0;
        for (int i = 0; i < 4; ++i)
        {
            dataLength |= buf.readUnsignedByte() << i * 8;
        }
        int readLength = inflater.getTotalOut();
        if (dataLength != readLength)
        {
            throw new DecompressionException(
                    "Number of bytes mismatch. Expected: " + dataLength
                            + ", Got: " + readLength);
        }
        return true;
    }

    private void verifyCrc(ByteBuf in)
    {
        long crcValue = 0;
        for (int i = 0; i < 4; ++i)
        {
            crcValue |= (long) in.readUnsignedByte() << i * 8;
        }
        long readCrc = crc.getValue();
        if (crcValue != readCrc)
        {
            throw new DecompressionException("CRC value missmatch. Expected: "
                    + crcValue + ", Got: " + readCrc);
        }
    }

    /*
     * Returns true if the cmf_flg parameter (think: first two bytes of a zlib
     * stream) indicates that this is a zlib stream. <p> You can lookup the
     * details in the ZLIB RFC: <a
     * href="http://tools.ietf.org/html/rfc1950#section-2.2">RFC 1950</a>.
     */
    private static boolean looksLikeZlib(short cmf_flg)
    {
        return (cmf_flg & 0x7800) == 0x7800 && cmf_flg % 31 == 0;
    }
}
